Internal combustion engines may be equipped with a supercharging arrangement, wherein supercharging may provide a method for increasing power, in which the charge air used for the combustion process in the engine is compressed, as a result of which a greater mass of charge air can be supplied to each cylinder per working cycle. In this way, the fuel mass and therefore the mean pressure can be increased.
Supercharging is a suitable method for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In many cases, supercharging leads to an increase in volumetric power output and a more expedient power-to-weight ratio. If the swept volume is reduced, it is possible, given the same vehicle boundary conditions, to shift the load collective toward higher loads, at which the specific fuel consumption is lower. Supercharging of an internal combustion engine consequently assists may increase engine efficiency and decrease fuel consumption.
Some transmission configurations may provide downspeeding, whereby a lower specific fuel consumption is likewise achieved. In the case of downspeeding, use is made of the fact that a specific fuel consumption at low engine speeds is generally lower, in particular in the presence of relatively high loads.
Supercharging may be provided via an exhaust-gas turbocharger, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow may be fed to and expand in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy supplied by the exhaust-gas flow to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor delivers and compresses the charge air supplied to it, as a result of which supercharging of the at least one cylinder is obtained. A charge-air cooler may be provided in the intake system downstream of the compressor, wherein the charge-air cooler may cool the compressed air before directed the compressed air to one or more engine cylinders. The cooler lowers the temperature and thereby increases the density of the charge air, such that the cooler also contributes to improved charging of the cylinders, that is to say to a greater air mass. In effect, compression by cooling occurs.
A difference of an exhaust-gas turbocharger in relation to a supercharger, wherein the supercharger utilizes an auxiliary device to drive the compressor, may include that an exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases, whereas a supercharger draws the energy used for driving it directly or indirectly from the internal combustion engine and thus adversely affects, that is to say reduces, the efficiency, at least for as long as the drive energy does not originate from an energy recovery source.
If the supercharger is not one that can be driven by means of an electric machine, that is to say electrically, a mechanical or kinematic connection for power transmission may be arranged between the supercharger and the internal combustion engine.
The advantage of a supercharger in relation to an exhaust-gas turbocharger consists in that the supercharger can generate, and make available, a desired charge pressure at a greater range of engine operating conditions. That is to say, the supercharger may provide a desired charge pressure regardless of the operating state of the internal combustion engine, in particular regardless of the present rotational speed of the crankshaft. This applies in particular to a supercharger which can be driven electrically via an electric machine.
In previous examples, it is specifically the case that difficulties may be encountered in achieving an increase in power in some engine speed ranges via exhaust-gas turbocharging. A torque drop may observed in the event of a certain engine speed being undershot. Said torque drop is understandable if one takes into consideration that the charge pressure ratio is dependent on the turbine pressure ratio. If the engine speed is reduced, this leads to a smaller exhaust-gas mass flow and therefore to a lower turbine pressure ratio. Consequently, toward lower engine speeds, the charge pressure ratio may likewise decrease. This may result in a torque drop. It can be sought, using a variety of measures, to improve the torque characteristic of a supercharged internal combustion engine.
The internal combustion engine to which the present disclosure relates has at least one exhaust-gas turbocharger and an electrically driveable compressor.
The electrically driveable compressor is in this case shaped as an activatable compressor which is activated when desired to assist an exhaust-gas turbocharger in compressing the charge air. In the context of the present disclosure, provision is not made for using the electrically driveable compressor instead of the exhaust-gas turbocharging arrangement to generate the charge pressure. According to the disclosure, the electric drive compressor is arranged in the intake system downstream of the compressor of the at least one exhaust-gas turbocharger, and, in the context of a multi-stage compression or supercharging configuration, compresses charge error that has already been pre-compressed. That is to say, the exhaust-gas turbocharger may compress charge-air before the electrically driveable compressor.
According to some examples, for the purposes of bypassing the electrically driveable compressor, a bypass line may branch off from the intake system, with the formation of a first junction, between the electrically driveable compressor and the compressor of the at least one exhaust-gas turbocharger and which opens into the intake system, with the formation of a second junction, downstream of the electrically driveable compressor and in which a shut-off element is arranged.
In this way, the line system on the inlet side of the internal combustion engine, that is to say the intake system, is more complex than if bypassing lines were omitted. If the lines of the intake system are shortened, a line system is obtained which has small radii of curvature, at which the charge-air flow may be intensely deflected several times, possibly resulting in pressure losses in the charge-air flow, which may be disadvantageous and correspond to parasitic power losses. By contrast, a line system with less frequent and less intense diversion of the charge-air flow results in an intake system of relatively large volume, which comprises a sizing equal to a desired size for optimal efficiency and thus opposes the densest possible packaging of the drive unit in the engine bay of the vehicle.
The configuration of the intake system generally becomes more complex if an exhaust-gas recirculation arrangement is provided for recirculating exhaust gases from the outlet side to the inlet side.
The inventors have found a solution to at least partially solve the problems described above associated with exhaust-gas turbochargers and electrically driven compressors. In one example, the problems are at least partially solved by a supercharged internal combustion engine that comprises an intake system for the supply of charge air, an exhaust-gas discharge system for the discharge of exhaust gas, at least one exhaust-gas turbocharger which comprises a turbine arranged in the exhaust-gas discharge system and a compressor arranged in the intake system, the compressor being equipped with at least one impeller which is arranged on a rotatable shaft in a compressor housing, and the compressor housing having a charge-air-conducting flow duct which proceeds from an inlet region of the compressor and extends as far as downstream of the at least one impeller, and an electrically driveable compressor, which is arranged in the intake system downstream of the compressor of the at least one exhaust-gas turbocharger, wherein the compressor housing for the compressor of the exhaust-gas turbocharger has at least two outlet regions, the charge-air-conducting flow duct splitting downstream of the at least one impeller into at least two arm-like duct branches, and in each case one arm-like duct branch opening into an outlet region, a first outlet region being connected via the intake system to the electrically driveable compressor, and the second outlet region being connected via the intake system, bypassing the electrically driveable compressor, to the intake system downstream of the electrically driveable compressor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.